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✔ UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , DC 20549 FORM 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 or TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission file number 001-36103 TECOGEN INC . ( Exact name of Registrant as specified in its charter ) Delaware ( State or Other Jurisdiction of Incorporation or Organization ) 45 First Avenue Waltham , Massachusetts 02451 ( Address of Principal Executive Offices ) 04-3536131 ( IRS Employer Identification No. ) ( 781 ) 466-6400 Registrant's telephone number , including area code Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes ¨ No ý Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes ¨ No ý Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes ý No " Accelerated filer 0 Smaller reporting company Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes ý No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company or an emerging growth company . See the definitions of " large accelerated filer " , " accelerated filer " , " smaller reporting company " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Large accelerated filer Non - Accelerated Filer Emerging growth company If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Yes No X Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Act ) . Yes No ý As of June 30 , 2020 , the last day of the registrant's most recently completed second fiscal quarter , the aggregate market value of the voting and non - voting common equity held by non - affiliates was : $ 25,611,519 . Solely for purposes of this disclosure , shares of common stock held by executive officers and directors of the registrant as of such date have been excluded because such persons may be deemed to be affiliates . This determination of executive officers and directors as affiliates is not necessarily a conclusive determination for any other purposes . As of March 9 , 2021 , 24,850,261 shares of common stock , $ .001 par value per share , of the registrant were issued and outstanding .